Fresh water accounts for only 2.5% of Earth's water, yet it is vital for human civilization. What are our sources of fresh water? In the first of a two part series on fresh water, Christiana Z. Peppard breaks the numbers down and discusses who is using it and to what ends.

Did you know that only 1% of Earth's water is fresh and available for consumption? Fresh water is the world's most essential natural resource, but it's also one of the most threatened. National Geographic magazine's April issue celebrates and explores this important resource.